The present invention relates to a clutch cover assembly, in which a diaphragm spring is used as a spring for actuating the pressure plate.
Generally, in a friction clutch of a diaphragm spring type, a diaphragm spring is seated on a rear surface of a pressure plate for actuating the pressure plate. Actuation of the pressure plate presses a friction facing of a clutch disc onto a flywheel to engage the clutch.
As opposed to other types of compressible springs, a diaphragm spring has a characteristic that, in a condition in which the spring is compressed to some extent, the compression load temporarily increases in accordance with a reduction of the compressed length. On the other hand, when a facing of the clutch disc is worn to some extent, after use, the position of the pressure plate in the clutch engaged condition changes toward the flywheel side from an initial position, so that the compressed length of the diaphragm spring reduces from the initial value.
Therefore, when the facing is worn, the load applied by the diaphragm spring to the pressure plate increases, and thus, the pressing force between the friction facing and the flywheel increases. Consequently, temperature at the surface of the facing increases which causes abnormal wear of the facing. This also prevents smooth operation of the clutch.
In order to avoid the above disadvantages, an improved structure has been proposed in Japanese Utility Model application No. 57-55043 and corresponding U.S. Pat. No. 4,602,208; of common assignment with the instant application. In this structure, an adjustment spring which has a characteristics similar to that of a diaphragm spring is associated with the diaphragm spring so that a pressure plate may receive a load corresponding to the difference between the elastic forces of both springs.
However, since said adjustment spring is disposed at the vicinity of a fulcrum mechanism of the diaphragm spring, it may be difficult to locate the adjustment spring if there is not sufficient space at the vicinity of the fulcrum mechanism.
Accordingly, it is an object of the present invention to provide an improved clutch cover assembly, overcoming the abovenoted disadvantages.